bug#7117: 23.2.2 mangles terminal escape sequences

[Ryan Johnson <ryanjohn@ece.cmu.edu>]

  On 9/30/2010 4:59 PM, Eli Zaretskii wrote:
>> From: Ryan Johnson<ryanjohn@ece.cmu.edu>
>> Cc: 7117@debbugs.gnu.org
>>
>> At this point the symptom is easy enough to understand: sometimes
>> discard-input gets unlucky and chops the front off of a partly-arrived
>> escape sequence.
>>
>> The real question is, why would the command loop encounter errors and
>> need to discard input at all?
>>     [1] _longjmp()
>> =>[2] unwind_to_catch()
>>     [3] Fsignal()
>>     [4] xsignal()
>>     [5] xsignal0()
>>     [6] window_scroll()
> The only calls to xsignal0 I see in window_scroll (or, rather, in its
> subroutines) is to signal Qbeginning_of_buffer or Qend_of_buffer.
>
>>  From the above, it seems that scrolling past beginning or end of buffer
>> triggers an error, which I guess is somewhat justifiable.
> Indeed.  Perhaps we need some infrastructure to ignore errors in this
> case (I assume `ignore-errors' won't help).  Or maybe we should allow
> not to discard input when we signal an error.  Or maybe discard-input
> should be smarter, and not discard partial escape sequences?
One thing I don't get is, I've been using emacs over painfully slow ssh 
connections for literally years -- sometimes slow enough that keystrokes 
take visible time to echo. This was never really an issue before. In 
retrospect, it did pop up occasionally all along, but it was infrequent 
enough to hide in the shadow of xterm mouse escape sequences confusing 
emacs for x>95. Now it interferes with normal work. Is there some change 
that would have done this? I'm using the same bad internet connection as 
when I had emacs-22...

>> However, on a
>> very slow connection this morning mouse-clicking between or even within
>> buffers caused problems. Unfortunately, setting debug-on-error doesn't
>> seem to catch errors generated from C code.
>>
>> I could try to break on longjmp over another slow connection, but with
>> the number of times it gets called for other reasons this would be slow
>> going...
>>
>> Ideas?
> You could put a breakpoint in Fsignal, and see if the problems with
> mouse-clicking within buffers is also caused by signaling an error.
I'll try that next time it becomes annoying (it's hit-and-miss...)

Ryan